1. Field
One or more embodiments relate to a negative active material comprising lithium titanate oxide, a negative electrode comprising the same, a lithium secondary battery comprising the negative electrode, and a method of preparing the negative active material.
2. Description of the Related Technology
Lithium titanate oxide (Li4Ti5O12) is known as an electrode material for lithium secondary batteries. Li4Ti5O12 is less expensive and has a smaller change in volume during charging and discharging processes, as compared to other electrode materials. Thus, when the lithium titanate oxide is applied to lithium secondary batteries, it exhibits excellent rapid charge/discharge characteristics and high performances. Therefore, lithium titanate oxide is expected to be widely used as an electrode material for high-output batteries used in applications requiring rapid charge and discharge, such as hybrid electric vehicles.
Lithium titanate oxide, which draws much attention as an electrode active material for lithium ion secondary batteries, has little change in volume even after repetitive intercalation/deintercalation of lithium ions, thus being highly stable, and also has long lifetime. In addition, lithium titanate oxide has a higher charge/discharge potential, e.g., 1.5V (vs Li/Li+) than general carbonaceous electrode materials, and thus deposition of lithium ions which is caused by decomposition of an electrolyte and rapid charge/discharge does not occur.
For example, lithium titanate oxide has an operating voltage of about 1.3 to about 1.6 V, which is higher than that of general carbonaceous negative electrode materials, and has a reversible capacity of about 170 mAh/g. However, lithium titanate oxide enables rapid charge and discharge, barely undergoes an irreversible reaction, and has a very low heat of reaction, thus being highly stable. Lithium titanate oxide has a theoretical density of about 3.5 g/cm3, which is higher than the theoretical density of carbonaceous negative electrode materials, e.g., about 2 g/cm3, and thus capacity per volume of lithium titanate oxide is similar to that of carbonaceous negative electrode materials.
Conventionally, the size of lithium titanate oxide is reduced to fine particles, thereby expanding an active surface thereof, which leads to rapid diffusion of lithium ions, and thus lithium titanate oxide may be used as a high input/output material.